Enhanced catalyst and process for converting synthesis gas to liquid motor fuels

ABSTRACT

The conversion of synthesis gas to liquid molar fuels by means of a cobalt Fischer-Tropsch catalyst composition is enhanced by the addition of molybdenum, tungsten or a combination thereof as an additional component of said composition. The presence of the additive component increases the olefinic content of the hydrocarbon products produced. The catalyst composition can advantageously include a support component, such as a molecular sieve, co-catalyst/support component or a combination of such support components.

STATEMENT

The Government of the United States of America has rights to thisintention pursuant to Contract No. DE-AC22-81-C40077 awarded by the U.S.Department of Energy.

This application is a division of prior U.S. application Ser. No.625,372 filed 6-27-84, now U.S. Pat. No. 4,579,830.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the conversion of synthesis gas tohydrocarbons. More particularly, it relates to the conversion of suchsynthesis gas to C₅ ⁺ hydrocarbons suitable for use as liquid motorfuels.

2. Description of the Prior Art

It is well known in the art that synthesis gas, i.e., hydrogen andcarbon monoxide, can be converted to hydrocarbons in the presence of avariety of transition metal catalysts. Thus, certain Group VIII metals,particularly iron, cobalt, ruthenium and nickel, are known to catalyzethe conversion of CO and hydrogen, also referred to as syngas, tohydrocarbons. Such metals are commonly called Fischer-Tropsch catalysts.While the use of nickel preferentially produces methane upon conversionof syngas, the use of iron, cobalt and ruthenium tends to producehydrocarbon mixtures consisting of hydrocarbons having a larger carbonnumber than methane, as determined by a number of analytical meansincluding mass spectrographic analysis of individual components and theboiling point curve method. At higher reaction temperatures, allFischer-Tropsch catalysts tend to produce gaseous hydrocarbons, and itis readily feasible to select processing conditions to produce methaneas the principal product. At lower temperatures, and usually at higherpressures, however, iron, cobalt and ruthenium produce hydrocarbonmixtures consisting of larger hydrocarbons. These products usuallycontain very long straight-chain hydrocarbon molecules that tend toprecipitate as wax. Such wax material, boiling well beyond the boilingrange of motor fuels, typically constitutes a significant fraction ofthe product produced in such catalytic conversion operations.Fischer-Tropsch catalysts have not been advantageously employed in theproduction of liquid hydrocarbon motor fuels, therefore, insteadcommonly producing either principally gaseous hydrocarbons, on the onehand, or hydrocarbons containing an unacceptably large amount of wax onthe other. In addition, the gasoline boiling hydrocarbon fraction thathas been produced has an unacceptably low octane number.

In light of such circumstances, efforts have been made to improve theperformance of Fischer-Tropsch catalysts for use in various desiredsyngas conversions. For example, the Breck et al. patent, U.S. Pat. No.3,013,990, discloses the use of zeolitic molecular sieves containing aFischer-Tropsch catalyst as improved catalyst compositions. Thus, TypeA, X and Y molecular sieves loaded with iron or cobalt are shown to besuitable Fischer-Tropsch hydrocarbon synthesis catalysts, as for theproduction of methanol from syngas. Also with respect to the conversionof syngas, Fraenkel et al., U.S. Pat. No. 4,294,725, teach that zeolitesA and Y loaded with cobalt, incorporated by ion exchange and reducedin-situ with cadmium, serve as useful catalysts of the Fischer-Tropschtype. Those skilled in the art will appreciate that such catalystmaterials tend to be relatively expensive and, in any event, do notproduce hydrocarbon products advantageous for use as liquid motor fuels.

Efforts have also been made to improve Fischer-Tropsch catalystperformance by preparing intimate mixtures of Fischer-Tropsch metals,such as iron, with an acidic crystalline aluminosilicate, such as ZSM-5.The Chang et al. patents, U.S. Pat. No. 4,086,262, and U.S. Pat. No.4,096,163, disclose such catalyst compositions employed in theconversion of synthesis gas to hydrocarbon mixture useful in themanufacture of heating fuels, gasoline, aromatic hydrocarbons andchemical intermediates. When it is desired to convert syngasspecifically to hydrocarbons boiling in the jet fuel+diesel oil boilingrange, however, such an approach is not suitable, experiencing aneffective limitation at C₁₀ carbon number as was the case using ZSM-5 inmethanol conversion, as disclosed in the Owen et al. patent, U.S. Pat.No. 3,969,426.

While iron is the currently preferred Fischer-Tropsch catalyst componentfor use in syngas conversion operations, cobalt had originally beenpreferred because of its various desirable properties. Thus, cobalt hasa higher level of catalytic activity in syngas conversion operations aswell as a better selectivity to total motor fuels than is obtained usingiron. Cobalt has certain product quality disadvantages, however, thathave tended to discourage its use for syngas conversion operations.Thus, the hydrocarbon products obtained using cobalt catalysts aregenerally more paraffinic and waxy than the corresponding productsobtained using iron as the Fischer-Tropsch catalyst. Such waxy productsare much more difficult to upgrade, as by the use of a shape selectivecomponent in the Fischer-Tropsch catalyst composition in accordance withknown practice, than would be a more olefinic hydrocarbon conversionproduct of syngas conversion operations.

It is desirable, therefore, that improvements be made in the art toenable cobalt to be more advantageously employed as a Fischer-Tropschcatalyst for syngas conversion operations. The prior art developmentsrelating to the use of cobalt catalysts for applications other thanFischer-Tropsch catalysts do not appear relevant to the problemsassociated with the Fischer-Tropsch conversion of syngas to liquid motorfuels. Thus, cobalt-molybdenum catalysts supported on alumina are thecommonly employed commercial hydrotreating hydrode-sulfurization)catalysts. Such catalysts, generally containing 3-5% CoO and 15% MoO₃ onAl₂ O₃, are not particularly relevant to Fischer-Tropsch catalysis. Inanother area of prior art activity, molybdenum and tungsten have beenemployed in Fischer-Tropsch synthesis reactions.

At a 1982 Material Research Society meeting, A. Brenner reported the useof molybdenum and tungsten as Fischer-Tropsch metals. Thus, molybdenumsalts were reduced at a high temperature (1000° C.), and the reducedmolybdenum was found to act as a very low activity Fischer-Tropschmetal. A somewhat more active catalyst can be formed by reducingmolybdenum or tungsten carbonyl. Molybdic acid has also been tested as apromoter for iron Fischer-Tropsch catalysts as reported in theFischer-Tropsch and Related Synthesis by H. Storch, N. Golumbic and R.Anderson, John Wiley & Sons, N.Y. 1951, however, the molybdic acid didnot improve the activity of the iron catalyst. Storch et al alsoreported the testing of tungsten oxide promoters for ironFischer-Tropsch catalysts, said promoters resulting in a shift of theproduct distribution toward high wax yields.

It is generally known in the art that manganese is effective inincreasing the olefin content of hydrocarbon products obtained uponsyngas conversion using an iron Fischer-Tropsch catalyst. Manganese isnot effective, however, in producing more olefins when a cobaltFischer-Tropsch catalyst is employed. Despite the various activitiescarried out in the art as indicated above, there remains a desire in theart for improvements rendering cobalt a more satisfactoryFischer-Tropsch catalyst for syngas conversion than it is at the presenttime. What is thus desired in the art is the development of an additiveand/or an operating technique that will have a similar effect withrespect to cobalt as has manganese with respect to iron catalysts.

It is an object of the invention, therefore, to provide an improvedFischer-Tropsch catalyst composition for use in the conversion of syngasto liquid motor fuels.

It is another object of the invention to provide an improvedcobalt-based Fischer-Tropsch catalyst composition for said syngasconversion.

It is a further object of the invention to provide a cobaltFischer-Tropsch syngas conversion catalyst and process capable ofenhancing the olefinic content of the liquid hydrocarbon conversionproducts obtained.

With these and other objects in mind, the invention is hereinafterdescribed in detail, the novel features thereof being particularlypointed out in the appended claims.

SUMMARY OF THE INVENTION

The olefinic content of the hydrocarbon products obtained during syngasconversion operations using cobalt as a Fischer-Tropsch catalyst isincreased by the addition of a particular additive component to a cobaltcatalyst composition. The catalyst composition is advantageouslysupported by a molecular sieve co-catalyst/support component capable ofenhancing the desired conversion of syngas to liquid hydrocarbons usefulor capable of conversion to desired motor fuels.

DETAILED DESCRIPTION OF THE INVENTION

The objects of the invention are accomplished by the admixing of aparticular additive component with a cobalt-containing Fischer-Tropschcatalyst. Such additive is taken from the group consisting ofmolybdenum, tungsten and combinations thereof. As a result of the use ofsuch an additive, the use of cobalt as a syngas conversion catalyst isenhanced as the resulting hydrocarbon products obtained are found tohave a desirably higher olefinic content than is obtained in the absenceof the use of the additive component. The suitability of the productliquid hydrocarbons obtained for use as motor fuels is thereby enhancedby the practice of the invention in conjunction with the use of cobaltwith or without thorium promotion as a Fischer-Tropsch catalyst forsyngas conversion. The synthesis gas, or syngas, treated in accordancewith the practice of the invention generally comprises a mixture ofhydrogen and carbon monoxide, usually together with smaller amounts ofcarbon dioxide, methane, nitrogen or other components as is well knownin the art. Syngas is commonly produced by steam reforming ofhydrocarbons or by the partial oxidation of coal and petroleum deposits,or by similar gasification of other carbonaceous fuels such as peat,wood and cellulosic waste materials. The hydrogen/carbon oxide volumeratio of such syngas is desirably in the range of from about 0.2/1 toabout 6.0/1 prior to conversion to liquid motor fuels as hereindisclosed and claimed. This ratio can be adjusted, if desired, byreaction of carbon monoxide with steam in the well-known water-gas shiftreaction. If required, sulfur impurities can be removed from the syngasmixture by conventional means known in the art. It should also be notedthat the syngas as described herein includes art-recognized equivalents,such as mixtures of carbon monoxide and steam, or of carbon dioxide andhydrogen, that can provide synthesis gas mixture by in-situ reactionunder the operating conditions employed.

The invention as herein described is related to the use of cobaltadmixed with the additive component referred to above, preferablythorium-promoted and preferably with a support component, particularlyone that tends to further enhance the desired syngas conversion toliquid motor fuels as further described below. The additive componentcan be employed in an amount within the range of from about 1% to about50 mole % based on the total amount of cobalt metal and said additivecomponent in the catalyst composition, with an additive componentconcentration of from about 5% to about 25% being generally preferredfor many applications.

In the practice of the invention, the cobalt component and the additivecomponent can be combined in various ways, preferably by a method ofcombination that brings the cobalt component, i.e., thorium-promotedcobalt, and the additive component into intimate contact in the catalystcomposition. A generally preferred method of incorporation is toimpregnate the cobalt, preferably thorium-promoted cobalt, with asolution of a soluble molybdenum or tungsten compound. For example,ammonium heptamolybdate is a commercially available compound that isvery soluble and suitable for purposes of the invention.Thorium-promoted cobalt oxide is a preferred source of cobalt.Coprecipitation of molybdenum or tungsten with the cobalt is alsopossible, but the resulting catalyst does not appear to have theextended lifetime capability achieved with respect to the preferredembodiments of the catalyst composition. A physical mixing of the cobaltwith the additive component may also be possible, but is less likely tobe effective for the desired purpose and is generally less preferred.

Synthesis gas conversion operations can be carried out in the practiceof the invention with the Fischer-Tropsch catalyst composition as hereindisclosed and claimed at a reaction temperature within the range of fromabout 150° C. to about 400° C., preferably from about 240° C. to about320° C. The conversion operations can be carried out at any convenientpressure level, as from about 0 to about 1,000 psig, typically at fromabout 0 to about 350 psig.

While other promoter materials such as potassium and sodium are known inthe art, thorium is employed as a promoter for the cobalt metalcomponent in the practice of the invention. The most effective level ofpromotion appears to be obtained when about 15% ThO₂ is employed basedon the weight of cobalt metal employed. The concentration of thorium canvary, however, from about 0.1 to about 15%, and some of the ThO₂ can bereplaced with less expensive MgO provided that at least about 5% ThO₂ isretained for the desired promoter activity in preferred embodiments ofthe invention.

Prior to use of the Fischer-Tropsch catalyst composition in the syngasconversion process of the invention, the cobalt catalyst is reduced oractivated by techniques employing hydrogen alone or together with othertreating materials as is known in the art. For example, the catalyst maybe activated by first combining with a low H₂ /CO ratio gas, or with COalone, at a temperature in the range of about 250°-320° C. and apressure of from 0 psig to the synthesis gas pressure. The catalyst isthen further treated with hydrogen under similar temperature andpressure conditions. Further information regarding the preparation andactivation of Fischer-Tropsch catalysts is provided in the publishedart, as in CATAL, REV.-SCI. ENG. 21(2), 225-274 (1980), "TheFischer-Tropsch Synthesis in the Liquid Phase", by Herbert Kolbel andMiles Ralek, particularly pp. 242-247 thereof.

In preferred embodiments of the invention, the Fischer-Tropsch catalystcomposition desirably includes a support additive for saidthorium-promoted cobalt and additive component admixture. Inparticularly preferred embodiments, said support component comprises amolecular sieve co-catalyst/support component rather than an inertsupport component such as α-alumina. The presence of such a co-catalystmaterial facilitates the desired conversion of syngas to liquid motorfuels. An especially desirable co-catalyst/support component forpurposes of the invention comprises steam-stabilized, hydrophobiczeolite Y catalyst, sometimes referred to in the art as ultrahydrophobictype Y zeolites, or simply as UHP-Y zeolites. The cobalt, with orwithout thorium promotion, and the additive component may be positionedmainly in the large pores between the crystallites formed during theextrusion of the catalyst. It has also been found possible to place saidcobalt and said additive component substantially within the crystallitesof said UHP-Y zeolite as further discussed below. The Y zeolites used inthis invention are prepared by extensive steaming of the low-sodiumforms of zeolite Y substantially as described in Belgian Pat. No.874,373, issued Feb. 22, 1979. Such zeolites are organophilic zeoliticaluminosilicate compositions having a SiO₂ /Al₂ O₃ molar ratio equal toor greater than 4.5, and an essential X-ray powder diffraction patternof zeolite Y. Furthermore, the zeolites have a crystallographic unitcell dimension, a_(o), of less than 24.45 Angstroms, a sorptive capacityfor water vapor at 25° C. and a p/p_(o) value of 0.10 of less than 10.0weight percent. In preferred compositions, said unit cell dimension ofthe catalyst is from 24.20 to 24.35 Angstroms. In addition, the wateradsorption capacity at 25° C. and a p/p_(o) value of 0.10 is desirablyless than 6.0 or even 4.0 weight percent. More particularly, the SiO₂/Al₂ O₃ molar ratio for certain embodiments is from 4.5 to 20.0. In adesirable embodiment in which the UHP-Y zeolite is acid extracted asdiscussed below, the SiO₂ /Al₂ O₃ molar ratio may be extended up toabout 100 or more, as the alumina content of the zeolite is generallyreduced to less than about 3 weight % or even to about 1 weight % orless in practical commercial applications.

For the determination of the sorptive capacity of the hydrophobiczeolite Y compositions for any particular adsorbate, e.g. water, thetest zeolite sample is activated by preheating at 425° C. for 16 hoursat a pressure of 5 micrometers of mercury in a conventional McBainapparatus. The temperature of the sample is thereafter adjusted to thedesired value and contacted with the vapor of the test adsorbate at thedesired pressure.

The hydrophobic zeolites suitable for purposes of the invention, asdescribed above, have also been found especially suited for use asadsorbents in applications where it is desired to preferentially adsorborganic constituents from solutions or mixtures thereof with water. Inthe formation of synthesis gas by the distillation of coal for example,it is desirable, for environmental and economic reasons, to recover therelatively small portion of phenol present in the condensate fraction ofprincipally water that is produced therein. For this purpose, thecondensate can be contacted at ambient temperature with said hydrophobiczeolite that will selectively adsorb the phenol from said condensate.Such zeolites have also been found highly suitable for use as basematerials for catalyst compositions having important commercialapplications, e.g. in midbarrel hydrocracking catalyst compositions. TheUHP-Y zeolites described in particular detail in the Belgian patentreferred to above have been found active for the conversion of methanolto hydrocarbons ranging from methane to those boiling in the jet fueland diesel oil boiling range up to about C₂₂ material.

The invention is hereinafter described with reference to specificcomparative tests that are presented to illustrate the invention and theadvantages thereof. These illustrative comparative tests should not beconstrued, however, as limiting the scope of the invention as set forthin the appended claims.

EXAMPLE I

This example is presented as a comparative reference and is based on theconversion of syngas using a thorium-promoted cobalt catalyst supportedon a UHP-Y co-catalyst/support component without the admixture of anadditive component with said cobalt as in the practice of the inventionillustrated in Example II below. For purposes of this Example I, thecobalt metal component was prepared by precipitation upon the additionof a 10% excess of sodium carbonate solution to a stirred roomtemperature aqueous solution of 400 g. of cobalt nitrate, i.e.Co(NO₃)₂.6H₂ O. The cobalt oxide precipitate was washed with hot waterand dried at 110° C. overnight. It was then impregnated with a thoriumnitrate solution to provide a 15 wt. % thorium concentration, based onthe weight of cobalt, on the precipitate, which was then dried at 110°C.

This thorium-promoted cobalt metal component was formed as 1/8" silicabonded extrudate containing 15% CoO/ThO₂, 70% UHP-Y zeolite and 15% bywt. silica binder. The resulting extrudate was dried at 110° C. for twohours.

80 cc of this catalyst was loaded into an internal recirculationreactor, in which it was treated, for cobalt activation, with hydrogen,at 300 psig, from room temperature up to 350° C., where it was held for24 hours before cooling to 270° C. for treatment with 1:1 syngas. THesyngas was fed to the reactor at a rate of 400 cc/min or 300 GHSV, i.e.gas hourly space velocity, or volume of gas (at 0° C., 1 atm)/volumecatalyst/hour. The conversion reaction was carried out at a pressure ofabout 300 psig and at a temperature of about 270° C. The resultsobtained in terms of the conversion of syngas, the primary productselectivity between hydrocarbons and CO₂, the hydrocarbon selectivity tothe desirable C₅ ⁺ range and other pertinent product characterizationsare as set forth below, including Table I, under the various operatingconditions recited in the Table.

                  TABLE I                                                         ______________________________________                                        Run          1       2       3     4     5                                    ______________________________________                                        Hours on Stream                                                                            19.5    115.5   139.5 163.5 187.5                                Temperature, °C.                                                                    272     269     269   270   269                                  Feed, cc/min.                                                                              400     400     400   400   400                                  Conversion, wt. %                                                             on CO        62.86   44.21   39.12 40.43 38.31                                on H.sub.2   89.40   72.07   66.43 67.26 65.97                                on (CO + H.sub.2)                                                                          75.66   58.36   52.78 53.81 52.12                                Product Selectivity, wt. %                                                    CH.sub.4     14.67   19.66   23.12 22.63 24.15                                C.sub.2 -C.sub.4                                                                           13.23   12.86   15.47 13.70 14.59                                C.sub.5 -420° F.                                                                    50.41   42.22   38.71 41.04 39.90                                420-700° F.                                                                         19.19   20.35   16.74 16.65 15.78                                700° F.-end Point                                                                    2.51    4.91    5.95  5.98  5.58                                C.sub.5 -end point                                                                         72.10   67.48   61.41 63.67 61.26                                Iso/Normal Mole Ratio                                                         C.sub.4      0.2857  0.1226  0.1778                                                                              0.1370                                                                              0.1327                               C.sub.5      0.5572  0.2546  0.2698                                                                              0.2540                                                                              0.2473                               C.sub.6      0.9660  0.4117  0.4181                                                                              0.4006                                                                              0.3892                               Paraffin/Olefin Ratio                                                         C.sub.3      0.6912  1.4156  1.1943                                                                              1.2831                                                                              1.2776                               C.sub.4      0.4206  0.7010  0.7044                                                                              0.6503                                                                              0.6289                               C.sub.5      0.5004  0.7141  0.6954                                                                              0.6438                                                                              0.6146                               ______________________________________                                    

Those skilled in the art will appreciate that the gasoline end point isabout 420° F., while the diesel oil end point is about 200° F. It willalso be appreciated that the 420°-700° F. hydrocarbon material comprisesmolecules with more carbon atoms than C₁₀ hydrocarbons up to about C₂₂material. Hydrocarbon material in the C₂₂ -C₂₈ range generally comprisesheavy distillate material, with material above C₂₈ generally comprisingwax.

The catalyst of this example showed an initial deactivation and anincrease in methane production. The selectivity to condensed productswas high, but the condensed products obtained contained undesired solidstherein. The total condensed product was distilled and fractionated intogasoline (initial boiling point -420° F.), jet fuel (300°-550° F.) anddiesel oil (300°-700° F.) fractions. The gasoline fraction contained36.4% olefins upon FIA, i.e., Florescence Indicator Absorption analysis.Under such analysis, the jet fraction contained 31.6% olefins and had apour point of 0° F. It will be appreciated that the pour point is thelowest temperature at which the liquid will flow. The diesel fractionhad a pour point of 50° F. With such a high pour point, the diesel oilfraction could not be pipelined at low temperature.

EXAMPLE II

In this comparative example illustrating the practice of the invention,the adsorbent composition was prepared as in Example I above, exceptthat the thorium-promoted cobalt component was impregnated with asolution of ammonium heptamolybdate to provide a 15% by weightdeposition of molybdenum on the CoO/ThO₂ component. The thus-impregnatedFischer-Tropsch metal component was dried and formulated into anextruded catalyst as in said Example I. The catalyst loading,pretreatment and testing for syngas conversion were also essentially asset forth in Example I. The results obtained are set forth in Table IIbelow:

                                      TABLE II                                    __________________________________________________________________________    Run         1   2    3   4    5   6    7   8    9   10                        __________________________________________________________________________    Hours on Stream                                                                           17.0                                                                              74.0 122.0                                                                             146.0                                                                              185.0                                                                             215  258.5                                                                             307.5                                                                              354.8                                                                             426.0                     Temperature, °C.                                                                   270 269  270 270  270 270  270 269  269 269                       Feed, cc/min.                                                                             400 400  400 400  400 400  400 400  400 400                       Conversion, wt. %                                                             on CO       67.21                                                                             55.09                                                                              51.71                                                                             51.48                                                                              49.81                                                                             48.82                                                                              48.47                                                                             44.98                                                                              43.85                                                                             42.02                     on H.sub.2  82.61                                                                             77.73                                                                              75.32                                                                             75.35                                                                              74.06                                                                             73.00                                                                              72.46                                                                             69.44                                                                              68.54                                                                             67.52                     on (CO + H.sub.2)                                                                         75.19                                                                             66.84                                                                              63.93                                                                             63.82                                                                              62.42                                                                             61.41                                                                              60.98                                                                             57.65                                                                              56.63                                                                             55.20                     Product Selectivity                                                           CH.sub.4    14.00                                                                             17.04                                                                              18.34                                                                             18.20                                                                              19.99                                                                             20.41                                                                              20.34                                                                             21.47                                                                              22.74                                                                             24.00                     C.sub.2 -C.sub.4                                                                          16.08                                                                             18.20                                                                              18.89                                                                             18.51                                                                              19.21                                                                             19.61                                                                              19.13                                                                             21.41                                                                              21.88                                                                             22.57                     C.sub.5 -420° F.                                                                   50.88                                                                             48.12                                                                              48.39                                                                             48.01                                                                              46.34                                                                             46.61                                                                              47.62                                                                             45.44                                                                              43.74                                                                             42.56                     420° F.-700° F.                                                             16.31                                                                             14.33                                                                              12.41                                                                             13.20                                                                              12.45                                                                             11.45                                                                              11.01                                                                              9.89                                                                               9.93                                                                              9.30                     700° F.-end point                                                                   2.73                                                                              2.31                                                                               1.97                                                                              2.07                                                                               2.01                                                                              1.92                                                                               1.90                                                                              1.79                                                                               1.70                                                                              1.57                     C.sub.5 -end point                                                                        69.92                                                                             64.76                                                                              62.77                                                                             63.29                                                                              60.80                                                                             59.98                                                                              60.53                                                                             57.12                                                                              55.38                                                                             53.43                     Iso/Normal Mole Ratio                                                         C.sub.4     0.2051                                                                            0.1383                                                                             0.1154                                                                            0.1083                                                                             0.0963                                                                            0.1000                                                                             0.0914                                                                            0.0448                                                                             0.0815                                                                            0.0771                    C.sub.5     0.4293                                                                            0.2618                                                                             0.2199                                                                            0.2101                                                                             0.1680                                                                            0.1634                                                                             0.1573                                                                            0.1414                                                                             0.1522                                                                            0.1412                    C.sub.6     0.8211                                                                            0.4066                                                                             0.3208                                                                            0.2929                                                                             0.2642                                                                            0.2527                                                                             0.2294                                                                            0.2181                                                                             0.2079                                                                            0.1174                    Paraffin/Olefin Ratio                                                         C.sub.3     1.1915                                                                            0.9740                                                                             0.9481                                                                            0.9506                                                                             0.9195                                                                            0.9303                                                                             0.9297                                                                            0.9590                                                                             0.9077                                                                            0.8321                    C.sub.4     0.6064                                                                            0.4851                                                                             0.4752                                                                            0.4787                                                                             0.4719                                                                            0.4615                                                                             0.4685                                                                            0.4617                                                                             0.4648                                                                            0.4650                    C.sub.5     0.7138                                                                            0.5197                                                                             0.4852                                                                            0.4779                                                                             0.4687                                                                            0.4648                                                                             0.4672                                                                            0.4665                                                                             0.4918                                                                            0.5468                    __________________________________________________________________________

It will be seen from the results of Example II as compared with those ofExample I, the catalyst of the invention did not show the rapid initialdeactivation and increase in methane selectivity seen in the use of thereference catalyst of Example I. The C₄ hydrocarbons will be seen to bemuch more olefinic than in Example I, and the paraffin/olefin ration inthe Example II runs tends to decline appreciably and then remainrelatively constant over the course of a relatively long period of onstream performance, whereas the ratio tends to increase appreciably andthen to level off in the reference runs of Example I. The condensedliquid samples of Example II were combined and distilled into gasoline,jet and diesel oil fractions as in Example I. The gasoline fractioncontained 48.3% olefins and the jet fraction contained 43.6% olefins,both significantly higher amounts were obtained in the reference runs ofExample I. The pour point of the jet fraction is -10° F., and that ofthe diesel oil is 20° F., again representing significant improvements ascompared to the reference runs. It will thus be appreciated that theprocess and catalyst composition of the invention provide a convenientand effective means for achieving the objects stated above, namely theimproving of syngas conversion operations by enhancing the olefiniccontent of the liquid hydrocarbon conversion products obtained. Thesignificant advantages obtained by the practice of the invention withrespect to the olefinic content of the liquid products is furtherenhanced when the Fischer-Tropsch catalyst composition contains amolecular sieve material therein, as in the comparative examples, sincethe molecular sieve can act upon olefins much easier than it can actupon paraffins for the production of more desirable liquid motor fuelmaterials.

Those skilled in the art will appreciate that various changes andmodifications can be made in the details of the invention withoutdeparting from the scope of the invention as set forth in the appendedclaims. Thus, as noted above, the desired enhancement of the olefiniccontent of the liquid hydrocarbon products can be facilitated by the useof a modified UHP-Y co-catalyst/support component or by the use of othersuch desirable support components. For example, the UHP-Y zeolitereferred to above can be employed in aluminum-extracted form.Furthermore, the cobalt and said additive component can be positionedsubstantially within the crystallites of the UHP-Y zeolite or of thealuminum-extracted form thereof, and not merely within the large poresbetween the crystallites formed during extrusion of the catalyst, thusenhancing catalyst stability. In general when a co-catalyst/support isemployed, the cobalt metal component will be employed in an amountwithin the range of from about 1% to about 25% by weight based on theoverall weight of the catalyst composition, with cobalt concentrationsof from about 5% to about 15% being generally preferred for mostapplications. When a co-catalyst/support component is not employed, fromabout 1% to about 100% cobalt by weight is useful, based on the totalweight of cobalt, inert metal and possibly other additives, with about5% to about 50% cobalt being preferred.

For purposes of achieving the aluminum-extracted form of said UHP-Yzeolite, the zeolite is conveniently acid washed or extractedessentially by the process as described in the Eberly patent, U.S. Pat.No. 3,591,488, to remove a large portion of the alumina from its poresprior to treatment to incorporate the metal component therein. Byemploying a suitable cobalt-containing liquid, such as cobalt carbonylor a solution of cobalt nitrate or other cobalt salt, the metal can bepositioned substantially within the crystals, and absorbed therein toform a very stable co-catalyst/support composition highly advantageousfor the purposes of the invention. In an illustrative example, UHP-Ymolecular sieve zeolite was refluxed in a 13% slurry of said sieve in3.75M hydrochloric acid for three hours. The slurry was then cooled, andthe supernatent was decanted therefrom. The remaining slurry was dilutedin half, filtered and washed chloride free with 0.001 of nitric acid.The slurry was then washed with distilled water, dried at 110° C. for 16hours and then at 250° C. for 16 hours and at 500° C. for an additionaltwo hours and bottled at 400° C. The thus-treated material comprisedacid-extracted, substantially alumina-free, or aluminum-extracted, UHP-Yzeolite.

In preparing the catalyst composition of the invention in embodimentsincluding a co-catalyst/support component, the cobalt metal component,promoted and admixed with said additive component, can be physicallymixed with the co-catalyst/support component, as in the examples above,or can be precipitated on or pore filled on said co-catalyst/supportcomponent. For purposes of positioning the cobalt within the crystals ofUHP-Y zeolite or the aluminum-extracted form thereof, a suitable cobaltsolution can be loaded onto the zeolite by impregnation followed byheating or treatment with base. Addition of the inert metal and/or thethorium can be accomplished either during cobalt impregnation orseparately thereafter.

Another advantageous co-catalyst/support component for purposes of theinvention is a crystalline, microporous SAPO silicoaluminophosphate,non-zeolitic molecular sieve catalyst. Such catalyst materials, known asSAPOs and available at Union Carbide Corporation, are described in U.S.Pat. No. 4,440,871, issued Apr. 3, 1984, incorporated in its entiretyherein. Individual members of the SAPO class are designated as SAPO-5,SAPo-11, SAPO-17, SAPO-20, SAPO-31, SAPO-34 and the like as disclosed insaid patent. SAPO-11 and SAPO-31 are generally preferred for purposes ofthe invention, although it will be appreciated that other SAPOs, orcombinations thereof alone or with other molecular sieves, may also beemployed. It is, for example, within the scope of the invention toemploy a steam-stabilized, hydrophobic zeolite Y, i.e. UHP-Y, as anadditional co-catalyst/support component in addition to said SAPOmaterial. In particular embodiments, the cobalt and said additivecomponent admixed therewith are positioned inside said zeolite Ycomponent, as for example inside the crystallites of thealuminum-extracted form thereof, with the thus-loaded UHP-Yco-catalyst/support component being used together with said SAPO orother suitable co-catalyst/support component.

It will be appreciated that such specific embodiments are intended toachieve the desired increase in the olefinic content of the liquidproducts obtained upon syngas conversion employing catalyst compositionsof desirable stability and catalytic activity favorable to theproduction of the desired liquid motor fuels. In such specificembodiments and more generally, the invention utilizes a modification ofcobalt not previously appreciated, in the context of syngas conversionand of the need for increasing the olefinic content of the productsobtained, as providing the desired advance in the production of motorfuels from such syngas. The invention thus enables the hydrocarbonproducts of the Fischer-Tropsch syngas conversion reaction to be moreolefinic than they would otherwise be using the Fischer-Tropsch catalystas employed, but without the addition of molybdenum or tungsten as anadditive component. The invention thus represents a desirable advance inthe art, enhancing the production of liquid motor fuels from syngas inan advantageous manner in light of the continuing need to meet the motorfuel requirements of industrial societies throughout the world.

I claim:
 1. A process for the enhanced catalytic conversion of synthesisgas comprising carbon monoxide and hydrogen to C₅ ⁺ hydrocarbon mixturesadvantageous for use as liquid motor fuels comprising contacting saidsynthesis gas with a Fischer-Tropsch catalyst composition comprisingcobalt, with or without thorium promotion, admixed with an additivecomponent taken from the group consisting of molybdenum, tungsten andcombinations thereof, said additive component being present in an amountwithin the range of from about 1% to about 50 mole % based on the totalamount of cobalt and said additive component in said composition,whereby the presence of said additive component increases the olefiniccontent of the hydrocarbon products obtained, thereby enhancing thesuitability of the resulting liquid hydrocarbons for use as motor fuels.2. The process of claim 1 in which the concentration of said additivecomponent is from about 5% to about 25%.
 3. The process of claim 1 inwhich said synthesis gas conversion is carried out at a reactiontemperature of from about 150° C. to about 400° C.
 4. The process ofclaim 3 in which said reaction temperature is from about 250° C. toabout 320° C.
 5. The process of claim 1 in which said additive componentcomprises molybdenum.
 6. The process of claim 1 in which said additivecomponent comprises tungsten.
 7. The process of claim 1 in which saidadditive component comprises a combination of molybdenum and tungsten.8. The process of claim 5 in which the concentration of said molybdenumis from about 5 to about 25%, said conversion reaction temperature beingfrom about 150° C. to about 400° C.
 9. The process of claim 8 in whichsaid reaction temperature is from about 240° C. to about 320° C.
 10. Theprocess of claim 1 in which said Fischer-Tropsch catalyst compositionincludes a support component for said cobalt and said additivecomponent.
 11. The process of claim 10 in which said support componentcomprises a molecular sieve co-catalyst/support component.
 12. Theprocess of claim 11 in which said co-catalyst/support componentcomprises a steam-stabilized, hydrophobic zeolite Y catalyst.
 13. Theprocess of claim 12 in which said additive component comprisesmolybdenum.
 14. The process of claim 12 in which saidco-catalyst/support component comprises said zeolite Y inaluminum-extracted form, said cobalt and said additive component beingpositioned substantially within the crystallites of saidaluminum-extracted zeolite.
 15. The process of claim 14 in which saidadditive component comprises molybdenum and said conversion reactiontemperature is from about 150° C. to about 400° C.
 16. The process ofclaim 15 in which said reaction temperature is from about 240° C. toabout 320° C.
 17. The process of claim 11 in which saidco-catalyst/support component comprises a crystalline, microporous SAPOsiliconaluminophosphate, non-zeolitic molecular sieve catalyst.
 18. Theprocess of claim 17 in which said SAPO catalyst comprises SAPO-11. 19.The process of claim 17 in which said SAPO catalyst comprises SAPO-31.20. The process of claim 17 in which said additive component comprisesmolybdenum.
 21. The process of claim 17 in which said additive componentcomprises tungsten.
 22. The process of claim 17 and including asteam-stabilized, hydrophobic zeolite Y additional co-catalyst/supportcomponent.
 23. The process of claim 22 in which said SAPO catalystcomprises SAPO-11.
 24. The process of claim 23 in which said zeolite Ycomponent is in aluminum-extracted form.
 25. The process of claim 24 inwhich the alumina content of said aluminum-extracted zeolite is lessthan about 3 weight %.
 26. The process of claim 25 in which theconcentration of said additive component is from about 5% to about 25%and said conversion reaction temperature is from about 150° C. to about400° C.
 27. The process of claim 26 in which said additive componentcomprises molybdenum.
 28. The process of claim 1 in which said cobalt ispromoted with thorium.
 29. The process of claim 8 in which said cobaltis promoted with thorium.
 30. The process of claim 11 in which saidcobalt is promoted with thorium.